Atmosphere learning device for oxygen concentration sensor

ABSTRACT

An atmosphere learning device performs atmosphere learning upon an output value from an oxygen concentration sensor based on the output value from the sensor when an exhaust passage is in an atmospheric state. The device includes a stop request determination device, an opening-closing valve control device, and a learning execution device. The stop request determination device is for determining whether an operation stop request of an engine has been made. The opening-closing valve control device is for controlling an opening-closing valve into a predetermined valve-opening state when it is determined by the determination device that the operation stop request has been made. The learning execution device is for executing the atmosphere learning after control of the opening-closing valve into the predetermined valve-opening state by the control device.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2009-236063 filed on Oct. 13, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an atmosphere learning device for an oxygen concentration sensor. In particular, the present invention relates to an atmosphere learning device that performs atmosphere learning on an output value from an oxygen concentration sensor, which detects oxygen concentration in exhaust gas from an internal combustion engine.

2. Description of Related Art

Conventionally, an oxygen concentration sensor (i.e., air/fuel ratio sensor) for exhaust gas discharged from an internal combustion engine is known. The oxygen concentration sensor detects oxygen concentration (air/fuel ratio) in this exhaust gas. This oxygen concentration sensor is configured such that an element current passing through a sensor element changes in accordance with the oxygen concentration in exhaust gas. In the engine, based on a measuring result of the element current passing through the sensor element, control of air-fuel ratio is performed.

In the oxygen concentration sensor, an output error may be caused because of such as production tolerance or aged deterioration. Accordingly, it is conventionally proposed to perform “atmosphere learning” by the oxygen concentration sensor during a fuel cut period, such as while a vehicle is being decelerated. More specifically, it is proposed to perform calibration for a relationship between an output value of the oxygen concentration sensor and the oxygen concentration by regarding a value measured by the oxygen concentration sensor during this fuel cut period as a value corresponding to the oxygen concentration of the atmosphere, i.e., to perform “atmosphere learning” on the oxygen concentration sensor (see, e.g., JP-A-2003-003903).

However, it takes sufficient scavenging time for an exhaust passage to be put into an atmospheric state after an execution start of the fuel cut. Accordingly, the fuel cut period is sometimes terminated prior to completion of the atmosphere learning. Therefore, sufficient time for appropriate implementation of the atmosphere learning while the vehicle is being driven by the engine is not necessarily secured. On the other hand, if the atmosphere learning is not performed, the calibration of the relationship between the output value of the sensor and the oxygen concentration cannot be done. As a result, there is concern that accuracy of detection of the oxygen concentration is reduced.

SUMMARY OF THE INVENTION

The present invention addresses at least one of the above disadvantages. Thus, it is a main objective of the present invention to provide an atmosphere learning device for an oxygen concentration sensor that appropriately performs atmosphere learning on an oxygen concentration sensor and that eventually improves accuracy of detection of oxygen concentration.

To achieve the objective of the present invention, there is provided an atmosphere learning device for an oxygen concentration sensor. The device is adapted for an internal combustion engine that includes a combustion chamber, an exhaust passage, an opening-closing valve, and the sensor. The opening-closing valve is configured to regulate a state of one of intake of gas into the combustion chamber and exhaust of gas from the combustion chamber. The sensor is provided for the exhaust passage to detect an oxygen concentration in exhaust gas. The device is configured to perform atmosphere learning upon an output value from the sensor based on the output value from the sensor when the exhaust passage is in an atmospheric state. The atmosphere learning includes calibration of a relationship between the output value from the sensor and the oxygen concentration. The device includes a stop request determination means, an opening-closing valve control means, and a learning execution means. The stop request determination means is for determining whether an operation stop request of the engine has been made. The opening-closing valve control means is for controlling the opening-closing valve into a predetermined valve-opening state when it is determined by the determination means that the operation stop request has been made. The learning execution means is for executing the atmosphere learning after control of the opening-closing valve into the predetermined valve-opening state by the control means.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a diagram generally illustrating an entire configuration of an engine control system in accordance with a first embodiment of the invention;

FIG. 2 is a flow chart illustrating a procedure for atmosphere learning processing in accordance with the first embodiment;

FIG. 3 is a timing diagram illustrating a specific mode of atmosphere learning in the system in accordance with the first embodiment;

FIG. 4 is a diagram illustrating a relationship between a valve overlap amount and a scavenging time required in accordance with a second embodiment of the invention;

FIG. 5 is a flow chart illustrating a procedure for atmosphere learning processing in accordance with the second embodiment; and

FIG. 6 is a timing diagram illustrating a specific mode of atmosphere learning in an engine control system in accordance with the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A first embodiment of the invention will be described below with reference to the accompanying drawings. In the present embodiment, the invention is embodied in a control device in an engine control system applied to an in-vehicle multiple cylinder engine. In the control system, control of fuel injection quantity and control of ignition timing, for example, are performed with an electronic control unit (hereinafter referred to as an ECU) serving as a center.

In an engine 10 in FIG. 1, an air cleaner 12 is provided at an uppermost stream portion of an intake pipe 11 (intake passage), and an airflow meter 13 for detecting the amount of suction air is provided on a downstream side of the air cleaner 12. A throttle valve 14, whose degree of opening is regulated by a throttle actuator 15 such as a direct-current (DC) motor, is provided on a downstream side of the airflow meter 13. The throttle valve 14 adjusts a passage sectional area of an intake passage of the engine 10. The degree of opening of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor integrated into the throttle actuator 15. A surge tank 16 is provided on a downstream side of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting intake pipe pressure is provided for the surge tank 16. An intake manifold 18, through which air is introduced into each cylinder of the engine 10, is connected to the surge tank 16. An electromagnetically-driven injector 19, which injects and supplies fuel, is attached to a portion of the intake manifold 18 near an intake port of each cylinder.

An intake valve 21 and an exhaust valve 22 are provided respectively at the intake port and an exhaust port of the engine 10. The intake valve 21 and the exhaust valve 22 (intake and exhaust valves 21, 22) are of an engine-driven type that opens or closes in accordance with rotation of the engine 10. More specifically, cam shafts 27, 28 rotate in accordance with the rotation of the engine 10, so that cams (not shown) attached to the cam shafts 27, 28 are rotated. As a result of the rotations of the cams, the intake valve 21 and the exhaust valve 22 are opened or closed. By the open operation of the intake valve 21, air-fuel mixture is introduced into a combustion chamber 23. By the open operation of the exhaust valve 22, exhaust gas after its combustion is discharged into an exhaust pipe 24 (exhaust passage).

Variable valve mechanisms 25, 26, which vary opening-closing time (valve timing) of the valves 21, 22, are provided respectively for the intake valve 21 and the exhaust valve 22. In the variable valve mechanisms 25, 26, an operating oil pump (not shown) is driven by torque of the engine 10, and accordingly, oil pressure of a hydraulic circuit (not shown) is controlled. As a result, valve timing of the intake valve 21 and the exhaust valve 22 is adjusted by the mechanisms 25, 26. In the present embodiment, phases of the cam shafts 27, 28 relative to an engine output shaft (crankshaft) are varied, so that the valve timing for at least one of the intake valve 21 and the exhaust valve 22 is changed. As a result of the change of valve timing, the amount of overlap between a valve opening period of the intake valve 21 and a valve opening period of the exhaust valve 22 (valve overlap amount) is changed.

An ignition plug 29 is attached to a cylinder head of the engine 10 for each cylinder. A high voltage is applied to the ignition plug 29 through an ignition device (not shown) including an ignition coil at desired ignition timing. As a result of the application of high voltage, a spark discharge occurs between counter electrodes of each ignition plug 29, and the air-fuel mixture introduced into the combustion chamber 23 is ignited for the combustion.

A catalyst 31 for purifying, for example, carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) in emission gas, such as a three-way catalyst, is provided for the exhaust pipe 24. An oxygen concentration sensor 32 for detecting an air/fuel ratio (oxygen concentration) of the air-fuel mixture with exhaust gas as a detection object is provided at the exhaust pipe 24 on an upstream side of the catalyst 31. More specifically, the oxygen concentration sensor 32 is a global detection type of air/fuel ratio sensor that outputs a global air/fuel ratio signal proportional to the oxygen concentration in the emission gas upon voltage application to a sensor element.

In addition, a coolant temperature sensor 34 for detecting coolant temperature, a crank angle sensor 35 for outputting a crank angle signal having a rectangular shape every specified crank angle of the engine 10 (e.g., with a period of 30° C. A), a cam angle sensor 36 for outputting a rectangular cam angle signal every predetermined cam angle, and so forth, are attached to the control system. Furthermore, for example, an air conditioner and an alternator, which are not shown, are provided as engine auxiliary machinery, and these auxiliaries are driven by the torque of the engine 10.

An electronic control unit (ECU) 40 is, as is well known, configured with a microcomputer 41 serving as a main constituent of the ECU 40. The microcomputer 41 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an electrically erasable and programmable ROM (EEPROM) and so forth. By executing various kinds of control programs stored in the ROM, the ECU 40 performs various controls of the engine 10 in accordance with engine operating state in each case. More specifically, respective signals are inputted into the microcomputer 41 of the ECU 40 from, for example, an ignition switch (IG switch) 51, in addition to the above-described various sensors. Based on the various signals, the microcomputer 41 calculates the fuel injection quantity and the ignition timing. Accordingly, the microcomputer 41 controls drives of the injector 19 and the ignition device or controls the opening and closing timing of the intake and exhaust valves 21, 22.

The control of the opening and closing timing of the intake and exhaust valves 21, 22 is described below in detail. The ECU 40 calculates target valve timing of the intake and exhaust valves 21, 22 based on outputs from various sensors for detecting the engine operating state, such as the intake pipe pressure sensor 17 and the coolant temperature sensor 34. The ECU 40 calculates actual valve timing of the intake and exhaust valves 21, 22 based on outputs from the crank angle sensor 35 and the cam angle sensor 36. By controlling the oil pressure in the hydraulic circuit of the variable valve mechanisms 25, 26, the ECU 40 changes the phases of the cam shafts 27, 28 of the intake and exhaust valves 21, 22. Consequently, the actual valve timing coincides with the target valve timing.

A battery 54 is connected to the ECU 40 via a switch 53 of a main relay 52. When an ON signal is inputted into the ECU 40 through the IG switch 51, the ECU 40 energizes a relay drive coil 55 of the main relay 52 and turns on the switch 53 so that electric power is supplied from the battery 54 to the ECU 40. The electric power, which is supplied via the main relay 52 from the battery 54, is supplied also to the actuator such as the throttle valve 14 besides the ECU 40. The main relay 52 continues to be maintained in an ON state for a predetermined time after the IG switch 51 is turned off. During this period of the ON state of the main relay 52, the electric power supply from the battery 54 to the ECU 40 is continued even after the IG switch 51 has been turned off.

In the present embodiment, the ECU 40 performs atmosphere learning as processing for doing calibration of a relationship between a sensor output value and oxygen concentration upon the oxygen concentration sensor 32. Specifically, the atmosphere learning is the following processing. That is, the ECU 40 determines that the vicinity of the oxygen concentration sensor 32 has an oxygen concentration that approximates the atmosphere in a period during which fuel supply to the engine 10 is stopped while a vehicle is in operation (e.g., fuel cut period while the vehicle is being decelerated). Then, the ECU 40 calibrates the relationship between the sensor output value and oxygen concentration based on an output value from the oxygen concentration sensor 32 at the time of the determination. Even more specifically, the atmosphere learning may be performed as follows. For example, during the implementation of the fuel cut as well as when a predetermined time has elapsed since a start of execution of the fuel cut, the ECU 40 reads out an output value Vatm from the oxygen concentration sensor 32. From a ratio between the read output value Vatm and a reference output value Vstd in an atmospheric state which is stored beforehand in the ROM, the ECU 40 calculates a learnt value Flea (=Vstd/Vatm). The learnt value Flea is stored in a backup memory such as the EEPROM or a backup RAM. Then, using the learnt value Flea obtained through the atmosphere learning, an actual output value Vaf from the oxygen concentration sensor 32 is converted into a value Vlea that does not include an output error due to, such as production tolerance or time degradation by means of the following equation (1).

Vlea=Vaf×Flea  equation (1)

However, while the vehicle is in operation, such as in the fuel cut period, the operational state of the engine 10 changes accordingly. Therefore, a sufficiently-long fuel cut period cannot be secured, and the atmosphere learning may not be performed after the IG switch 51 is turned on until the IG switch 51 is turned off. More specifically, exhaust gas remains in the exhaust pipe 24 immediately after the fuel cut start. Thus, it takes sufficient scavenging time to put the inside of the exhaust pipe 24 into the atmospheric state after the start of execution of the fuel cut. For this reason, even though the fuel cut has been started, the fuel cut may be ended before the atmosphere learning is completed due to, such as operation of an accelerator of the vehicle, and combustion control may thereby be resumed. In such a case, the relationship between the sensor output value and oxygen concentration cannot be calibrated. Moreover, if a period during which the atmosphere learning is not performed is prolonged, accuracy of detection of oxygen concentration by the oxygen concentration sensor 32 may be reduced in this period.

Accordingly, in the present embodiment, the atmosphere learning is performed in an operation stopped state of the engine 10. More specifically, when a request to stop operation of the engine 10, such as turn-off operation of the IG switch 51, is made, the intake and exhaust valves 21, 22 and the throttle valve 14, which serve as opening-closing valves for adjusting a state of suction/discharge of gas into/from the combustion chamber 23 of the engine 10, are controlled into a predetermined valve-opening state for promotion of the scavenging of an exhaust system, and after that, the atmosphere learning is performed. As a result, after the scavenging of the exhaust passage is promoted in the operation stopped state of the engine 10, the atmosphere learning is performed. Meanwhile, specifically, valve-opening control of the intake and exhaust valves 21, 22 is carried out such that the sum of valve opening amounts in a state in which the intake valve 21 and the exhaust valve 22 are opened at the same time after the rotation of the engine 10 is stopped, coincides with a predetermined amount of scavenging promotion. Particularly, in the present embodiment, by maximizing the valve overlap amount between the intake and exhaust valves 21, 22 after the stop of the rotation of the engine 10, the sum of valve opening amounts is set at the predetermined amount of scavenging promotion. Furthermore, by putting the throttle valve 14 into a fully open state, the scavenging of the exhaust passage is performed as efficiently as possible after the stop of the rotation of the engine 10.

The processing illustrated in FIG. 2 is performed with a predetermined period by the ECU 40. This processing is executed by the electric power supply from the battery 54 to the ECU 40 in accordance with an ON state of the main relay 52 being maintained for a predetermined time after the IG switch 51 is turned off.

In FIG. 2, at step(S) 101, whether a value 0 (zero) is set at a valve-opening execution flag FVL is first determined. The valve-opening execution flag FVL is a flag indicating that a command signal for putting the intake and exhaust valves 21, 22 and the throttle valve 14 into the predetermined valve-opening state for promotion of the scavenging has been outputted after the IG switch 51 is turned off. In the case of this command having been outputted, the flag FVL is set at a value 1.

If the command for putting the intake and exhaust valves 21, 22 and the throttle valve 14 into the predetermined valve-opening state has not yet been outputted, positive determination is made at S101 and control thereby proceeds to S102, at which it is determined whether the IG switch 51 has just been switched from an ON state to an OFF state. In the case of the timing of switching of the IG switch 51 from ON into OFF, the processing at S103 to S106 is performed.

More specifically, at S103, the throttle valve 14 is controlled in the predetermined valve-opening state. In the present embodiment, the throttle valve 14 is put in a fully open state. At S104, by changing rotation phases of the cam shafts 27, 28 relative to the crankshaft through the control of oil pressure in the variable valve mechanisms 25, 26, the valve timing of the intake and exhaust valves 21, 22 is changed such that the valve overlap amount between the intake valve 21 and the exhaust valve 22 after the stop of the rotation of the engine 10 accords with the predetermined amount of scavenging promotion (i.e., maximum overlap amount in the present embodiment). For example, by the intake-side variable valve mechanism 25, the valve timing of the intake valve 21 is changed on an advance side, and by the exhaust-side variable valve mechanism 26, the valve timing of the exhaust valve 22 is changed on a retard side. In addition, by changing only the valve timing of the intake valve 21 on the advance side or by changing only the valve timing of the exhaust valve 22 on the retard side, the valve overlap amount may be set at the predetermined amount of scavenging promotion.

At S105, the stop position of the piston at the time of the stop of the rotation of the engine 10 is adjusted through the control of a stop position of the engine 10 such as drive control of the alternator, such that a stop position of any piston is located at an exhaust top dead center or vicinity thereof. After that, at S106, a value 1 is set at the valve-opening execution flag FVL.

At S107, whether the rotation of the engine 10 is stopped is determined based on an output value from the crank angle sensor 35, for example. If it is determined that the rotation of the engine 10 has been stopped, it is determined whether a predetermined scavenging time required has elapsed since the IG switch 51 has been turned off. This scavenging time required is set as enough time to take exhaust gas out of the exhaust passage and to replenish the exhaust passage with fresh air in a state in which the valve overlap amount is maximized and the throttle valve 14 is fully-opened.

If the required scavenging time has not elapsed yet since the IG switch 51 has been turned off, negative determination is made at S107, and the present processing is temporarily ended. On the other hand, if the required scavenging time has elapsed since the IG switch 51 has been turned off, control proceeds to S108 to perform the atmosphere learning. More specifically, the output value from the oxygen concentration sensor 32 after the lapse of the required scavenging time since the IG switch 51 has been turned off, is considered to be an output when the vicinity of the oxygen concentration sensor 32 is in the atmospheric state. Based on the ratio between this output value Vatm and the reference output value Vstd, the learnt value Flea is calculated, and the value Flea is stored in the backup memory. Then, the valve-opening execution flag FVL is reset at the value 0, and the present processing is ended.

A first diagram (IG) in FIG. 3 illustrates transition of ON/OFF of the IG switch 51. A second diagram (NE) in FIG. 3 illustrates change of a rotational speed of the engine 10. A third diagram (TH) in FIG. 3 illustrates transition of the degree of opening of the throttle valve 14. A fourth diagram (OL) in FIG. 3 illustrates transition of the valve overlap amount between the intake and exhaust valves 21, 22. A fifth diagram (ATMOSPHERE LEARNING) in FIG. 3 illustrates transition of execution/execution stop of the atmosphere learning.

In FIG. 3, when the IG switch 51 is turned off at timing t11, the throttle opening degree TH is changed to a fully open position, and the oil pressure in the variable valve mechanisms 25, 26 is controlled such that the valve overlap amount OL reaches a maximum value Lmax. In accordance with the turning off of the IG switch 51, the engine rotational speed NE gradually decreases, and at timing 12 after the valve overlap amount OL has reached the maximum value Lmax, the rotation of the engine 10 is stopped. When the required scavenging time TA has elapsed, from the turning-off timing t11 of the IG switch 51, execution of the atmosphere learning is started at timing t13 of the elapse of the time TA. In addition, after completion of the atmosphere learning, the throttle opening degree TH is maintained at a predetermined intermediate opening degree Tlmp for ensuring the amount of suction air for evacuation traveling (limphome).

According to the present embodiment described in detail above, the following excellent effects are produced.

If the turn-off operation of the IG switch 51 is performed, the intake and exhaust valves 21, 22 and the throttle valve 14 are controlled into the predetermined valve-opening state for promotion of the scavenging of the exhaust system, and after that, the atmosphere learning is carried out. Accordingly, there is no influence from change of the engine operating state in performing the atmosphere learning. As a result, a sufficient time necessary to scavenge the exhaust passage is secured, so that the atmosphere learning is performed under the condition in which the vicinity of the oxygen concentration sensor 32 is put in the atmospheric state. Therefore, the atmosphere learning is appropriately carried out, and accuracy of the detection of oxygen concentration is eventually improved.

In regard to the valve-opening states of the intake and exhaust valves 21, 22, valve-opening modes of the intake and exhaust valves 21, 22 are controlled such that, in the state in which the intake valve 21 and the exhaust valve 22 are opened at the same time after the stop of the rotation of the engine 10, the sum of valve opening amounts coincides with the predetermined amount of scavenging promotion; more specifically, the valve overlap amount between a valve-opening period of the intake valve 21 and a valve-opening period of the exhaust valve 22 is set at a predetermined amount. Accordingly, the amount of the fresh air introduced into the exhaust system is increased, and eventually, the scavenging of the exhaust system is efficiently performed.

The valve overlap amount between the intake and exhaust valves 21, 22 is maximized, and the throttle valve 14 is put into a fully open state. Accordingly, the scavenging of the exhaust passage is effectively conducted.

The throttle valve 14 is opened (full throttle) after the IG switch 51 has been turned off. Accordingly, compared to the case of the throttle valve 14 being not opened, a pump loss while the engine 10 is rotating through inertia is reduced, and a decreasing rate of the engine rotational speed NE after the turning off of the IG switch 51 is made small. As a result, a time for increasing the valve overlap amount after the turning off of the IG switch 51 is secured, and eventually, the scavenging of the exhaust system is efficiently performed.

Second Embodiment

A second embodiment of the invention will be described below with a focus on its different features from the first embodiment. In the first embodiment, the case of implementation of the atmosphere learning after the predetermined scavenging time required has elapsed since the IG switch 51 has been turned off has been described above. In the present embodiment, a scavenging state when exhaust gas in an exhaust passage after the stop of rotation of an engine 10 is replaced with fresh air is detected, and based on the detected scavenging state, a required scavenging time is variably set. Then, after the required scavenging time has elapsed since turning off of the IG switch 51, atmosphere learning is carried out. This is because in time of the exchange between exhaust gas and fresh air in the exhaust passage, when a comparison is drawn between a case of efficient implementation of the scavenging and a case of inefficient implementation of the scavenging, a time needed for the exhaust passage to be put into an atmospheric state differs.

Particularly, in the present embodiment, the valve overlap amount after the stop of rotation of the engine 10 is detected as the scavenging state, and based on the detected valve overlap amount, the required scavenging time is variably set.

Reasons for the above will be given as follows. That is, after the turning off of the IG switch 51, the oil pressure in the variable valve mechanisms 25, 26 decreases in accordance with reduction of a rotational speed of the engine 10. When an engine rotational speed is reduced to such a rotational speed that operating oil cannot be pressure-fed through a pump, an advancing change or a retarding change of valve timing stops at this point, so that the valve timing cannot be changed to target time. On the other hand, a rate of decrease of the engine rotational speed after the turning off of the IG switch 51 varies according to various operating conditions such as a machine error, a rotational load of the engine output shaft (e.g., drive status of the air conditioner or the alternator), engine friction, and the pump loss. For example, as the rotational load of the engine output shaft becomes larger, the engine rotational speed is more greatly reduced after the IG switch 51 is turned off. Thus, the valve overlap amount after the stop of rotation of the engine 10 can vary according to its operating conditions in each case. Moreover, because of the variation in the valve overlap amount, the scavenging state after the stop of rotation of the engine 10 can also vary. Accordingly, in the present embodiment, the scavenging time required is set in accordance with the valve overlap amount after the stop of rotation of the engine 10.

An example of a relationship between the valve overlap amount after the stop of rotation of the engine 10 and the required scavenging time, is illustrated in FIG. 4. As illustrated in FIG. 4, as the valve overlap amount after the stop of rotation of the engine 10 becomes smaller, the required scavenging time becomes longer.

For example, a time required since timing of turning off of the IG switch 51 until the stop of rotation of the engine 10 is measured, and based on this required stop time, the valve overlap amount after the stop of the engine 10 is estimated. In this case, as required stop time becomes shorter, the valve overlap amount after the stop of the engine 10 becomes smaller. Based on a parameter relating to the engine friction (e.g., engine water temperature) or a parameter relating to the rotational load of the engine output shaft (e.g., drive status of the air conditioner or the alternator), the valve overlap amount after the stop of rotation of the engine 10 is estimated. More specifically, given that as the engine friction or the rotational load of the engine output shaft becomes larger, the engine rotational speed after turning off of the IG switch 51 is more significantly reduced, as the engine friction or the rotational load becomes larger, the valve overlap amount after the stop of the engine 10 is made smaller. Or, based on the crank angle signal from the crank angle sensor 35 and the cam angle signal from the cam angle sensor 36, the valve overlap amount may be estimated. In addition, intake valve timing and exhaust valve timing at the time of the turning off of the IG switch 51 may be considered.

Processing in FIG. 5 is executed with a predetermined period by the ECU 40. This processing is executed by the electric power supply from the battery 54 to the ECU 40 in accordance with an ON state of the main relay 52 being maintained for a predetermined time after the IG switch 51 is turned off. In the following description, description of the processing similar to FIG. 2 will be omitted with the same step number as FIG. 2.

In FIG. 5, at S201, whether a value 0 (zero) is set at a time setting flag FTM is first determined. At S202, it is determined whether a value 0 (zero) is set at a valve-opening execution flag FVL. The time setting flag FTM is a flag indicating that the required scavenging time before the atmosphere learning is performed after the IG switch 51 is turned off has been set. If the required scavenging time has already been set, the time setting flag FTM is set at a value 1.

If the command for putting the intake and exhaust valves 21, 22 and the throttle valve 14 into the predetermined valve-opening state is not yet outputted, and the required scavenging time is not set, positive determination is made at S201 and S202. Then, at S203 to 206, the processing, which is similar to S102 to S104, and S106 in FIG. 2, is executed.

At S207, whether the rotation of the engine 10 is stopped is determined based on the output value from the crank angle sensor 35, for example. If it is determined that the rotation of the engine 10 has been stopped, at S208, the valve overlap amount after the stop of rotation of the engine 10 is detected as the scavenging state of the exhaust passage, and based on the detected valve overlap amount and a map in FIG. 4, a required time (required scavenging time) before execution of the atmosphere learning after the turning off of the IG switch 51 is set. Then, a value 1 is set at the time setting flag FTM.

At S209, whether the required scavenging time has elapsed after the turning off of the IG switch 51 is determined, and if the required scavenging time has not elapsed, the present processing is ended. If the required scavenging time has elapsed after the turning off of the IG switch 51, on the other hand, control proceeds to S210 to perform the atmosphere learning. Then, after the time setting flag FTM and the valve-opening execution flag FVL are reset at a value 0 (zero), the present processing is ended.

A first diagram to a fifth diagram in FIG. 6 are similar respectively to the first to fifth diagrams of FIG. 3. In FIG. 6, after the turning off of the IG switch 51, it is assumed that the rotation of the engine 10 is stopped before the valve overlap amount reaches a predetermined amount of scavenging promotion (maximum overlap amount).

In FIG. 6, when the IG switch 51 is turned off at timing t21, a throttle opening degree TH is put into a fully open state, and the valve timing is changed on an advance side or on a retard side through the control of oil pressure in the variable valve mechanisms 25, 26, so that a valve overlap amount OL reaches a maximum value Lmax. In accordance with the turning off of the IG switch 51, an engine rotational speed NE gradually decreases. When the rotational speed NE decreases to such a rotational speed that operating oil cannot be pressure-fed through a pump, an advancing change or a retarding change of valve timing is stopped at that timing t22, so that the valve overlap amount OL has a smaller value than the maximum value Lmax. In this case, a longer time TB than the case of the valve overlap amount OL being set at the maximum value Lmax, is set as the scavenging time required.

According to the present embodiment described in detail above, the following excellent effects are produced.

The scavenging state of the exhaust passage after the stop of rotation of the engine 10 is detected, and the required scavenging time is variably set based on the detected scavenging state. Accordingly, the required time before the execution of atmosphere learning is set in accordance with a degree of promotion of the scavenging of the exhaust passage. As a result, even in a state in which the scavenging of the exhaust passage cannot be efficiently performed, the atmosphere learning is carried out after waiting for the exhaust passage to be securely put into the atmospheric state.

Considering that because a decreasing rate of the engine rotational speed after the request to stop the engine 10 varies with various operating conditions, a variation is caused in the valve overlap amount after the rotation of the engine 10 is stopped, the valve overlap amount after the stop of rotation of the engine 10 is detected as the scavenging state of the exhaust passage after the stop of the engine 10, and the required scavenging time is set based on the detected valve overlap amount. Accordingly, regardless of the valve overlap amount after the stop of rotation of the engine 10, the atmosphere learning is carried out after waiting for the exhaust passage to be securely put into the atmospheric state.

Modifications of the above embodiments will be described below. The present invention is not limited to the description of the above embodiments, and may be embodied, for example, as follows.

In the above-described embodiments, in accordance with the turning off of the IG switch 51, the valve overlap amount is controlled through the engine-driven type variable valve mechanisms 25, 26, and the throttle valve 14 is put into a fully open state. However, this may be modified. That is, after the rotation of the engine 10 is stopped after the IG switch 51 is turned off, the valve overlap amount is controlled and the throttle valve 14 may be put into a fully open state. In this case, the variable valve mechanism 25 is of an electrical motor-driven type.

The valve overlap amount is controlled so that, in a state in which the intake valve 21 and the exhaust valve 22 are opened at the same time after the engine 10 is stopped, the sum of valve opening amounts coincides with a predetermined amount of scavenging promotion. Alternatively, a valve lift amount may be controlled so that the sum of valve opening amounts coincides with a predetermined amount of scavenging promotion.

In the above embodiments, by making variable the phase of the cam shaft, the valve overlap amount is changed. Alternatively, the valve overlap amount may be changed by making variable the valve lift amounts of the intake and exhaust valves 21, 22. Or, the valve overlap amount may be changed using both the phase of the cam shaft and the valve lift amounts.

In the second embodiment, the valve overlap amount after the stop of rotation of the engine 10 is detected as the scavenging state of the exhaust passage, and based on the detected valve overlap amount, the required scavenging time is variably set. Alternatively, instead of the valve overlap amount or in addition to the valve overlap amount, the valve lift amount after the stop of rotation of the engine 10 may be detected as the scavenging state of the exhaust passage, and based on the detected valve lift amount, the required scavenging time may be variably set.

In the second embodiment, the time before the atmosphere learning is performed after the IG switch 51 is turned off is regarded as the scavenging time required, and in accordance with the scavenging state of the exhaust passage, the required scavenging time is set. Alternatively, the required scavenging time may be defined as a time before the atmosphere learning is executed after at least one of the throttle valve 14 and the intake and exhaust valves 21, 22 is put into a predetermined valve-opening state. Or, the required scavenging time may be defined as a time before the atmosphere learning is performed after the rotation of the engine 10 is stopped. Therefore, the required scavenging time may be any period as long as it is that which indicates the time taken to put the exhaust passage into the atmospheric state before execution of the atmosphere learning, and any timing may be considered to be a starting point of the required scavenging time.

When the atmosphere learning is performed, the atmosphere learning may be performed with the throttle valve 14 set further on a closed side (e.g., a fully closed state or a limphome opening degree) than the fully open state. In this case, an exhaust flow rate in the exhaust passage becomes smaller than the throttle fully open state. Accordingly, a gas atmosphere around the oxygen concentration sensor 32 is stabilized, and the sensor output is made stable.

In the above embodiments, the variable valve mechanisms 25, 26 is of an engine-driven type that variably controls the valve timing as a result of the oil pressure of the hydraulic circuit being controlled through the operating oil pump driven by the torque of the engine 10. However, configurations of the variable valve mechanisms 25, 26 are not limited to the above. For example, the operating oil pump may be electrically-operated instead of the engine-driven type which is driven by the engine torque. Furthermore, instead of the configuration in which the valve timing is changed by the control of the oil pressure of the hydraulic circuit through the operating oil pump, a power-operated variable valve mechanism which changes the valve timing by electrically performing the rotations of the cam shafts 27, 28, for example may be applied to the present invention.

In the above embodiments, after the IG switch 51 is turned off, three opening-closing valves of the intake valve 21, the exhaust valve 22, and the throttle valve 14 are controlled into a predetermined valve-opening state. Alternatively, one or two opening-closing valve(s) of those valves may be controlled in the predetermined valve-opening state. In this case, a variable valve mechanism for a valve whose valve-opening mode is controlled only needs to be disposed.

In the above embodiments, the gasoline engine has been described. However, the engine 10 is not limited to a gasoline engine, and the present invention may be applied to a diesel engine.

The atmosphere learning device for the oxygen concentration sensor 32 in accordance with the embodiments of the invention is summarized as follows.

The present invention is applied to the engine 10 that includes the opening-closing valves 21, 22, 14 for adjusting a state of suction/discharge of gas into/from the combustion chamber 23 of the engine 10 and the oxygen concentration sensor 32 for detecting oxygen concentration in exhaust gas in the exhaust passage of the engine 10. The present invention relates to the atmosphere learning device for the oxygen concentration sensor 32 that performs the atmosphere learning on the output value of the sensor 32 based on the output value from the oxygen concentration sensor 32 when the exhaust passage is in an atmospheric state.

The atmosphere learning device is for an oxygen concentration sensor 32. The device is adapted for an internal combustion engine 10 that includes a combustion chamber 23, an exhaust passage, an opening-closing valve 21, 22, or 14, and the sensor 32. The opening-closing valve 21, 22, or 14 is configured to regulate a state of one of intake of gas into the combustion chamber 23 and exhaust of gas from the combustion chamber 23. The sensor 32 is provided for the exhaust passage to detect an oxygen concentration in exhaust gas. The device is configured to perform atmosphere learning upon an output value from the sensor 32 based on the output value from the sensor 32 when the exhaust passage is in an atmospheric state. The atmosphere learning includes calibration of a relationship between the output value from the sensor 32 and the oxygen concentration. The device includes a stop request determination means S102, S203, or 40, an opening-closing valve control means S103, S204, or 40, and a learning execution means S108, S210, or 40. The stop request determination means S102, S203, or 40 is for determining whether an operation stop request of the engine 10 has been made. The opening-closing valve control means S103, S204, or 40 is for controlling the opening-closing valve 21, 22, or 14 into a predetermined valve-opening state when it is determined by the determination means S102, S203, or 40 that the operation stop request has been made. The learning execution means S108, S210, or 40 is for executing the atmosphere learning after control of the opening-closing valve 21, 22, or 14 into the predetermined valve-opening state by the control means S103, S204, or 40.

Generally, the atmosphere learning for the oxygen concentration sensor 32 is carried out while the engine 10 is in operation, after waiting for an operational state of the engine 10 to be put into a state (e.g., fuel cut) in which an atmospheric state is formable in the exhaust passage. To put the inside of the exhaust passage into the atmospheric state, the above operational state needs to be continued for a predetermined time. However, since the operational state of the engine 10 varies on a case-by-case basis, the operational state does not continue for a sufficiently long time, and as a result, the atmosphere learning may not be performed.

In view of this, in the present invention, when a request to stop the operation of the engine 10 is made, the amount of gas flowing through the exhaust system of the engine 10 is increased by controlling the opening-closing valves 21, 22, 14 into a predetermined valve-opening state, and the exhaust passage is thereby scavenged. Then, the atmosphere learning is performed. If the operation of the engine 10 has been stopped, there is no influence from change of the engine operation state. Thus, a sufficient time necessary to scavenge the exhaust passage is secured, so that the atmosphere learning is performed under the condition in which the vicinity of the oxygen concentration sensor 32 is put in the atmospheric state. As a result, according to the present invention, the atmosphere learning is appropriately carried out, and accuracy of the detection of oxygen concentration is eventually improved.

The control of the opening-closing valves 21, 22, 14 after the request to stop the operation of the engine 10 may be started before rotation stop of the engine 10 or after the rotation stop of the engine 10, as long as it is started after the request to stop the operation has been made.

The engine 10 may further include an intake valve 21 and an exhaust valve 22. The opening-closing valve 21, 22, or 14 may include at least one of the intake valve 21 and the exhaust valve 22. As the control of the opening-closing valve 21, 22, or 14 into the predetermined valve-opening state, the control means S103, S204, or 40 may control a valve-opening mode of the at least one of the intake valve 21 and the exhaust valve 22 such that a sum of valve opening amounts of the intake valve 21 and the exhaust valve 22 in a state in which the intake valve 21 and the exhaust valve 22 are opened at a same time after an operation stop of the engine 10 reaches a predetermined amount for promotion of scavenging of the exhaust passage.

The valve opening amount may be controlled, for example, by changing the rotation phases of the cam shafts 27, 28 relative to the engine output shaft (crankshaft) or by changing the valve lift amount. The intake valve 21 and the exhaust valve 22 may be opened or closed through the engine-driven type mechanism for performing opening and closing operations by the torque of the engine 10 or through the electrically-operated mechanism.

As the control of the opening-closing valve 21, 22, or 14 into the predetermined valve-opening state, the control means S103, S204, or 40 may control the sum of valve opening amounts into the predetermined amount for promotion of scavenging by adjusting an amount OL of valve overlap during which a valve-opening period of the intake valve 21 and a valve-opening period of the exhaust valve 22 overlap.

By controlling the valve overlap amount, the sum of the valve opening amounts is increased, and eventually, the scavenging of the exhaust system is efficiently performed.

In the case of the exchange between exhaust gas that remains in the exhaust passage and fresh air (i.e., scavenging), the exhaust passage is put into the atmospheric state for a comparatively short time in a state in which the exchange between exhaust gas and fresh air is efficiently performable as well as in a good scavenging state. On the other hand, in a state of the exchange being inefficient and the scavenging state being not very good, a time needed for the exhaust passage to be put into the atmospheric state becomes longer. Therefore, when execution time for the scavenging is made the same between a case of efficient implementation of the scavenging and a case of inefficient implementation of the scavenging, the atmosphere learning may be performed despite the exhaust passage having not been put into the atmospheric state in the case of inefficient implementation of the scavenging.

The atmosphere learning device may further include a scavenging state detecting means S208, or 40 for detecting a scavenging state of the exhaust passage after a rotation stop of the engine 10; and a time setting means S208 or 40 for setting a required time TA or TB before execution of the atmosphere learning after predetermined timing that follows the operation stop request, based on the scavenging state detected by the detecting means S208 or 40.

The “predetermined timing,” which is a starting point of the “required time,” is not particularly limited as long as it is after the “operation stop request” and before an execution start timing for the atmosphere learning. For example, the “predetermined timing” may be defined as timing at which the opening-closing valves 21, 22, 14 have been put into a desired valve-opening state. Furthermore, the “predetermined timing” may be defined as timing at which the “operation stop request” for the engine 10 has been made. Or, the “predetermined timing” may be defined as timing for the stop of the rotation of the engine 10.

The device is adapted for the engine 10 which may further include an engine driven-type variable valve mechanism 25 or 26 that is configured to variably control valve timing for at least one of an intake valve 21 and an exhaust valve 22 of the engine 10. As the control of the opening-closing valve 21, 22, or 14 into the predetermined valve-opening state, the control means S103, S204, or 40 may adjust an amount OL of valve overlap, during which a valve-opening period of the intake valve 21 and a valve-opening period of the exhaust valve 22 overlap, through the variable valve mechanism 25 or 26. The detecting means S208 or 40 may detect the amount OL of valve overlap at a time of the rotation stop of the engine 10 as the scavenging state. The setting means S208 or 40 may set the required time TA or TB based on the amount OL of valve overlap detected by the detecting means S208 or 40.

A mechanism of an engine-driven type that variably controls the valve timing of the intake valve 21 or the exhaust valve 22 by controlling oil pressure, for example, through a pump driven by the torque of the engine 10, is generally known as the variable valve mechanism. In a system including the variable valve mechanism of such an engine-driven type, the oil pressure in the variable valve mechanism may decrease in accordance with the reduction of the engine rotational speed after the request to stop the engine 10, and an advancing change or a retarding change of the valve timing may be stopped before the valve timing reaches the target time. Because a decreasing rate of the engine rotational speed after the request to stop the engine 10 can vary according to various operating conditions, a variation occurs in the valve overlap amount after the stop of rotation of the engine 10. If the valve overlap amount after the rotation stop varies, a degree of promotion of the scavenging of the exhaust passage differs in accordance with the valve overlap amount. In this respect, as a result of the above-described configuration, by setting a required time before execution of the atmosphere learning in accordance with the valve overlap amount after the rotation stop, regardless of the valve overlap amount after the rotation stop, the atmosphere learning is carried out after waiting for the exhaust passage to be securely put into the atmospheric state.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. An atmosphere learning device for an oxygen concentration sensor, wherein: the device is adapted for an internal combustion engine that includes: a combustion chamber; an exhaust passage; an opening-closing valve that is configured to regulate a state of one of intake of gas into the combustion chamber and exhaust of gas from the combustion chamber; and the sensor that is provided for the exhaust passage to detect an oxygen concentration in exhaust gas; the device is configured to perform atmosphere learning upon an output value from the sensor based on the output value from the sensor when the exhaust passage is in an atmospheric state; and the atmosphere learning includes calibration of a relationship between the output value from the sensor and the oxygen concentration, the device comprising: a stop request determination means for determining whether an operation stop request of the engine has been made; an opening-closing valve control means for controlling the opening-closing valve into a predetermined valve-opening state when it is determined by the determination means that the operation stop request has been made; and a learning execution means for executing the atmosphere learning after control of the opening-closing valve into the predetermined valve-opening state by the control means.
 2. The atmosphere learning device according to claim 1, wherein: the engine further includes an intake valve and an exhaust valve; the opening-closing valve includes at least one of the intake valve and the exhaust valve; and as the control of the opening-closing valve into the predetermined valve-opening state, the control means controls a valve-opening mode of the at least one of the intake valve and the exhaust valve such that a sum of valve opening amounts of the intake valve and the exhaust valve in a state in which the intake valve and the exhaust valve are opened at a same time after an operation stop of the engine reaches a predetermined amount for promotion of scavenging of the exhaust passage.
 3. The atmosphere learning device according to claim 2, wherein as the control of the opening-closing valve into the predetermined valve-opening state, the control means controls the sum of valve opening amounts into the predetermined amount for promotion of scavenging by adjusting an amount of valve overlap during which a valve-opening period of the intake valve and a valve-opening period of the exhaust valve overlap.
 4. The atmosphere learning device according to claim 1, further comprising: a scavenging state detecting means for detecting a scavenging state of the exhaust passage after a rotation stop of the engine; and a time setting means for setting a required time before execution of the atmosphere learning after predetermined timing that follows the operation stop request, based on the scavenging state detected by the detecting means.
 5. The atmosphere learning device according to claim 4, wherein: the device is adapted for the engine which further includes an engine driven-type variable valve mechanism that is configured to variably control valve timing for at least one of an intake valve and an exhaust valve of the engine; as the control of the opening-closing valve into the predetermined valve-opening state, the control means adjusts an amount of valve overlap, during which a valve-opening period of the intake valve and a valve-opening period of the exhaust valve overlap, through the variable valve mechanism; the detecting means detects the amount of valve overlap at a time of the rotation stop of the engine as the scavenging state; and the setting means sets the required time based on the amount of valve overlap detected by the detecting means.
 6. The atmosphere learning device according to claim 1, wherein: the engine further includes an intake passage; the opening-closing valve is a throttle valve that is configured to regulate a passage sectional area of the intake passage; and the control means puts the throttle valve into a fully open state when it is determined by the determination means that the operation stop request has been made. 